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Full text of "The Morphology And Evolution Of The Apes And Man"

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EXTERNAL CHAEACTEES AND HABITS  67
of the nails is marked on all digits. And in the Hoolock Gibbon the claws are of considerable length. Possibly these variations depend on age and sex rather than on species. The terminal phalanges exhibit well-marked pads, and the thenar and hypothenar eminences vary in prominence. No rnetacarpal pads are present.
The skin of the palm exhibits a number of grooves known as flexure lines, for they are situated in the areas where the hand bends in gripping. In all species there are 'transverse lines over the interphalangeal joints, and a curved line of more or less depth encircles the thenar area, which is submitted to considerable compression in the act of opposing the thumb. Many variations in the line pattern are seen in the palm, but it is highly improbable that these would be of value for purposes of classification. The Bornean and White-handed Gibbons (fig. 19A) have transverse lines, but the Hoolock Gibbon has longitudinal lines and several irregular little grooves.
The whole of the palm and fingers is traversed by fine ridges running in different directions; and these elevations, which are known as papillary ridges, are produced by thickening of the epidermis over rows of derrnic papillae. They are mainly sensory in function, but their roughness helps to make the grip of the hand secure. It will be seen in fig. 19 that longitudinal lines traverse the palm from the wrist to the roots of the fingers in all species. In the Bornean Gibbon there are loops on the thenar and hypothenar areas, but the Hoolock and white-handed species have no trace of these curves. The apical pads on the thumb and fingers are covered by ridges arranged in loops, and the skin of the remaining